Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and apparatus for receiving acknowledgement/not-acknowledgement (ACK/NACK) indicating reception acknowledgement in a wireless communication system.
Related Art
One of the most important requirements of a next generation wireless communication system is to support a high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various techniques are partially used in a wide frequency band. For this reason, as a method of ensuring a broadband bandwidth for satisfying a required higher data rate, a carrier aggregation (CA) is introduced. In concept, the CA is designed such that a basic requirement which allows separate bands to operate respective independent systems, and a plurality of bands are aggregated into one system. In this case, a band that can be independently managed is defined as a component carrier (CC).
The latest communication standard (e.g., 3GPP LTE-A or 802.16m) considers to expand its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz. As such, a system supporting carrier aggregation is called a carrier aggregation system.
Meanwhile, a wireless communication system considers a system in which a base station supports a greater number of user equipments in comparison with the legacy system. For example, one base station may have to support the greater number of user equipments when a technique such as machine type communication (MTC), enhanced multi user multi input multi output (MIMO), etc., is applied.
In this case, it may be difficult to transmit control information to a plurality of user equipments when using only a physical downlink control channel (PDCCH) in long term evolution (LTE)) conventionally used to transmit the control information. This is because there may be a problem in that a radio resource of the PDCCH is insufficient or an interference becomes serious. In order to solve such a problem, it is considered to allocate a new control region to a radio resource region in which data is transmitted in the legacy system. Such a new control channel is called an enhanced-PDCCH (E-PDCCH).
Meanwhile, a base station transmits acknowledgement/not-acknowledgement (ACK/NACK) for uplink data received from a user equipment through a physical hybrid-ARQ indicator channel (PHICH). The PHICH is located in a region to which a conventional control channel, i.e., PDCCH, is allocated. The PHICH may also have a radio resource shortage problem or an interference problem when the number of user equipments supported by the base station is increased and a carrier aggregation is supported. Therefore, it is considered to introduce a new channel for ACK/NACK transmission, and such a channel is called an enhanced-PHICH (E-PHICH).
However, even if a wireless communication system supports the E-PDCCH and the E-PHICH, the E-PDCCH and the E-PHICH may not be included in all user equipments, all carriers, and all subframes. That is, the E-PDCCH and the E-PHICH may be selectively used. In addition, when the carrier aggregation is supported, multiple carriers may be allocated to a specific user equipment.
In this case, it is necessary to regulate which carrier and which channel will be used by the user equipment to receive ACK/NACK. That is, in which way the base station will transmit ACK/NACK and how the user equipment will receive the ACK/NACK may become a matter to be discussed.